1. Field of the Invention
The present invention relates to the field of ophthalmology, and particularly to an improved design for haptics for an intraocular lens ("IOL"), the haptics being suitable for implantation of an appropriate optic in either a phakic or an aphakic eye.
2. Description of the Related Art
Ophthalmologists have been developing the art of implanting an artificial lens in the human eye for many years, both to replace the natural lens which has been removed due to disease (an aphakic eye), and to supplement the natural lens with a corrective lens (a phakic eye).
Various pathologic disease processes can cause deterioration of the natural lens requiring removal of the lens, most notably the opacification of the lens which occurs in cataracts. In the developmental stage, cataracts may be treated by frequent changes of eyeglass prescription. When useful vision is lost, the natural lens is generally removed, either intact or by emulsification. When the lens has been removed, correction is achieved either through spectacles, contact lenses, or an intraocular implant.
Common vision problems include myopia (nearsightedness) hypermetropia (hyperopia or farsightedness) and astigmatism. Traditionally such vision problems have been treated with corrective lenses in spectacles or contact lenses. However, as significant improvements and experience has been gained, the use of intraocular implants using corrective lenses has increased.
Generally, the lens separates the aqueous humor from the vitreous body. The iris separates the region between the cornea or anterior of the eye and the lens into an anterior chamber and a posterior chamber. The lens itself is contained in a membrane known as the capsule or capsular sac. When the lens is removed from the eye, the capsule may also be removed (intracapsular excision), or the anterior portion of the capsule may be remove with the lens leaving the posterior portion of the capsule intact (extracapsular extraction), often leaving small folds or flaps from the anterior portion of the capsule. In an intraocular implant, the artificial or prosthetic lens may be inserted in the anterior chamber, the posterior chamber, or the capsular sac. The artificial lenses are usually fixedly attached within the eye, either by stitching to the iris, or by some supporting means or arms attached to the lens, often in the form of sweeping arms called haptics.
In the late 1970's, several intraocular lenses designed for implant in the anterior chamber were developed by D. Pater Choyce. U.S. Pat. No. 4,087,866, issued May 9, 1978, is an example. The lens features four haptics with feet which support the lens in order to avoid the need for clips or sutures to secure the lens to the iris. The lenses designed by Choyce worked; however, sizing the lens to fit the eye was critical to avoid complications. The lenses were made in lengths from 11.5 mm to 14 mm in 0.5 mm increments, and the thickness of the feet were about 250 microns.
A variety of lenses have been developed by C. D. Kelman. In U.S. Pat. No. 4,174,543, issued Nov. 20, 1979, Kelman taught that although the haptics of many prior art patents provided four point support for the lens, the support structures for the haptics were often linked to the lens body so that the support structure could not deflect freely of the lens body, and is therefore liable to irritate portions of the eye in contact with the support structure (col. 1, lines 48-62). The '543 patent described haptics which included a pair of limbs joined to the lens body by stems so that the limbs would deflect independently, the limbs terminating in contact lobes which have a thickness of 0.2 mm (200 microns).
A variety of other shapes and geometries for the lens supporting elements, or haptics, have been disclosed, including: U.S. Pat. No. 4,254,510, issued Mar. 10, 1981 to J. L. Tennant;, U.S. Pat. No. 4,363,143, issued Dec. 14, 1982 to W. B. Callahan; U.S. Pat. No. 4,480,340, issued Nov. 6, 1984 to D. D. Shepard; U.S. Pat. No. 4,504,981 to G. B. Walman; U.S. Pat. No. 4,536,895, issued Aug. 27, 1985; U.S. Pat. No. 4,575,374, issued Mar. 11, 1986 to T. Bittner; U.S. Pat. No. 4,581,033, issued Apr. 8, 1986 to W. B. Callahan; U.S. Pat. No. 4,629,460, issued Dec. 16, 1986 to R. L. Dyer; U.S. Pat. No. 4,676,792, issued Jun. 30, 1987 to D. Praeger; U.S. Pat. No. 4,701,181, issued Oct. 20, 1987 to E. J. Arnott; U.S. Pat. No. 4,778,464, issued Oct. 18, 1988 to Sergienko, et al.; U.S. Pat. No. 4,787,902, issued Nov. 29, 1988 to Sheets, et al.; U.S. Pat. No. Re. 33,039, issued Aug. 29, 1989 to E. J. Arnott; U.S. Pat. No. 4,872,876, issued Oct. 10, 1989 to J. M. Smith; U.S. Pat. No. 5,047,052, issued Sep. 10, 1991 to S. Dubroff; and U.K. Patent No. 2,165,456, published Apr. 16, 1986.
Despite the advances, there remain problems with intraocular implants which may be ameliorated by the improved haptics and method of releasing the haptics of the present invention inside the bulb of the eye. When an intraocular lens is inserted in the eye, an incision is made in the cornea or sclera. The incision causes the cornea to vary in thickness, leading to an uneven surface which causes astigmatism. The insertion of a rigid lens through the incision, even with compressible haptics, requires an incision large enough to accommodate the rigid lens (at least 6 mm), and carries with it the increased risk of complications, such as infection, laceration of the ocular tissues, and retinal detachment. Deformable intraocular lenses made from polymethylmethacrylate ("PMMA"), polysulfone, silicone or hydrogel may be inserted through a smaller incision, about 4 mm.
It is therefore desirable that the intraocular lens be capable of insertion through a small incision. U.S. Pat. No. 4,451,938, issued to C. D. Kelman, shows an intraocular lens in which the lens body is made in two pieces so that each piece may be inserted through the incision separately and then joined by dowels after insertion in the eye. U.S. Pat. No. 4,769,035, issued Sep. 6, 1988, also to Kelman, discloses a foldable lens which may be inserted through an incision about 3.5 mm in length.
When the intraocular lens is inserted in the anterior chamber of the eye, the feet of the haptics, or lens supporting elements, generally lodge in the scleral sulcus, a depression anterior to the scleral spur where the iris and the ciliary muscle join the sclera in the angle of the anterior chamber. The scleral sulcus is crossed by trabecular tissue in which the spaces of Fontana are located. The anterior chamber of the eye is filled with the aqueous humor, a fluid secreted by the ciliary process, passing from the posterior chamber to the anterior chamber through the pupil, and from the angle of the anterior chamber it passes into the spaces of Fontana to the pectinate villi through which it is filtered into the venous canal of Schlemm. The lens must be positioned so the flow of fluid through the trabecular tissue is not blocked or glaucoma may result.
Since the feet of the haptics rest in the scleral sulcus, the flow of fluid will be blocked where the feet are in contact with the trabecular tissue. It is therefore desirable to decrease the amount of surface area of the haptic foot in contact with the trabecular tissue. At the same time, the haptic feet must have sufficient height to prevent adhesive tissue or synechia from growing around the feet and anchoring them to the iris or cornea The opening of the trabecula is about 200 microns. The haptic feet of conventional intraocular lenses are usually on the order of 175 to 200 microns, effectively blocking the openings in the trabecula wherever the feet are in contact with the tissue. U.S. Pat. Nos. 5,258,025 and 5,480,428, issued Nov. 2, 1993, and Jan. 2, 1996, respectively, to Federov, et al., describes a lens surrounded by a sheet-like "positioner" having projections called "supporting elements either at the four corners of or continuously around the positioner, the supporting elements being 0.3 mm long and 0.01 to 0.05 mm thick (7"a and 7"b of FIG. 3 of the '025 patent, 18 of the '428 patent). However, the lens described by Federov is for implantation in the posterior chamber, the lens of the '428 actually having a length short enough to "float". In addition, the sheet-like nature of the positioner prevents independent deflection the feet in response to forces applied by the eye.
In addition, the lens may place a greater or lesser degree of force on the haptic feet as the lens is compressed, depending upon construction of the lens. Since the amount of pressure for a given surface area is proportional to the force, it is desirable to decrease or distribute the amount of force placed on the haptic feet in order to diminish the force applied by the feet on the trabecular tissue. The present invention achieves this goal by mounting the haptic arms on the ends of a flexible support bar in cantilever fashion, the support bar being offset from the lens body by a stem. Applicant is not aware of any similar haptic design in the prior art.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a haptics for an intraocuplar lens solving the aforementioned problems is desired.